Battery packs containing one or more batteries or cells are used in many applications, e.g. telecommunications, grid, mobile, and/or any other suitable applications. As a battery pack is used and the batteries therein age, the batteries may need to be balanced and/or monitored with respect to their states of charge, e.g. their end-of-discharge voltage. The state of charge (SOC) of a battery, as used herein, is generally defined as the percentage of the full capacity of a battery that is still available for further discharge. Similarly, the end-of-discharge (EOD) voltage of a battery generally refers to a voltage level corresponding to the critical level of charge within the battery. Any further discharge beyond this critical level may cause a high risk of damage to the cells of the battery. Moreover, both due to aging effects and inaccuracies associated with direct monitoring of SOC, it is desirable to end the discharge of the battery based on the voltage level. Thus, to protect the battery from over-discharging, most devices prevent operation beyond a specified end-of-discharge voltage.
Conventional methods for detecting end-of-discharge of a battery utilize unreliable and indirect measurements such as charge, SOC, and/or resistance. Still further conventional methods utilize voltage and/or power thresholds; however, such methods are not typically accurate or reliable due to voltage polarization. More specifically, voltages of the batteries tend to have at least some transient behaviors under dynamic loads, which can make detection of end-of-discharge very challenging. Thus, the dynamic variations in voltage may result in either an over-discharge condition or an early termination of the discharge. An additional problem that exists with conventional methods is that during normal cell aging, the resistance profile of the cells tends to increase.
In view of the aforementioned issues, it is desirable to provide an improved system and method for detecting battery end-of-discharge that is accurate and persistent, especially when the battery is excited by a dynamic load. In addition, a system and method for detecting battery end-of-discharge that is insensitive to aging would be advantageous.